The wiring patterns formed on the circuit board are conventionally used to transmit and receive electrical signals to an integral circuit (IC) and a semiconductor component mounted on the circuit board, or other electronic components. The wiring patterns as described above are formed to be less resistant as the formation of the wiring patterns becomes more fine and complicated in association with recent miniaturization of the electronic components. As described above, as the miniaturization of the wiring patterns on the circuit board progresses, higher accuracy is required to inspect the quality of the wiring patterns, or whether the wiring patterns are non-defective or defective.
As a method of inspecting the quality of the wiring patterns, there are broadly two types of inspection: conduction inspection for inspecting whether the wiring patterns are formed with a predetermined resistance value, and insulation inspection for inspecting whether each wiring pattern is formed without a short-circuit.
In particular, the insulation inspection is to inspect an insulation state from a resistance value between wiring patterns, which is calculated by applying a voltage to one of the wiring patterns and by measuring a current flowing in the other wiring pattern.
In the insulation inspection as described above, immediately after a predetermined voltage (or applied voltage V) is applied to the one wiring pattern, a voltage between the wiring patterns is unstable and a high transient current instantaneously flows between the wiring patterns. Thus, the voltage between the wiring patterns is stabilized at the applied voltage V. Moreover, the quality of the insulation state is determined after an elapsed time (or a predetermined time) in which the current is stabilized. However, the application of a relatively high direct current voltage (or applied voltage) between the wiring patterns as the inspection objects sometimes causes a spark (or a discharge phenomenon) between the wiring patterns before the predetermined time elapses after the application of the voltage. The spark changes an insulation resistance value between the wiring patterns, and this complicates the calculation of a correct insulation resistance value between the wiring patterns, which is problematic.
In order to improve the problem, for example, a technology disclosed in Japanese Patent No. 3546046 can be used. In the technology disclosed in Japanese Patent No. 3546046, the spark is detected by measuring a variation in voltage between the wiring patterns during the predetermined time in which the applied voltage is applied to the wiring patterns and by detecting a voltage drop when the spark occurs as described above. For example, a graph illustrating a voltage change in FIG. 10 of Japanese Patent No. 3546046 indicates that the spark occurs at a time point t21 and a time point t22 in the graph. As described above, the spark is detected by detecting the voltage change and by detecting the voltage drop caused by the spark (or a value obtained by calculating “dv/dt”) (at positions of A and B in the graph).
Since the circuit board as described above is mass-produced, it is important how to efficiently inspect the mass-produced circuit boards and complete the inspection. Therefore, a method of reliably and efficiently performing the insulation inspection is required.